We think this is a software bug that Microsoft should look into. It has happened on one of our client’s computers (Lenovo i5, Windows 7 Pro, MS Office Home & Business 2016, for very simple and light use) from time to time. We have not found a permanent solution yet, but we do have some quick fixes as below, which may stop this problem from coming back for a few weeks.
1. Start Outlook in “Safe Mode” and close it. Then start Outlook normally.
This is the easiest way to work around this problem.
To start Outlook in “Safe Mode”, you will need to click “Start”, type outlook.exe /safe in the Run or Search box, then hit “Enter”.
(There is a space before the forward slash)
2. Delete the OST file
Go to the folder “C:\Users\the-user-name\AppData\Local\Microsoft\Outlook”, find the file whose extension name is OST, delete this file. Then start Outlook again.
3. Delete the Outlook profile and re-create one.
We found that the followings did not help with this problem
1. “Quick Repair” and “Online Repair” Office 2016
2. Uninstall and reinstall Office 2016
By the way, we also tried to format the hard drive and reinstall everything from scratch, but the problem still came back.